1) Field
Embodiments relate to the field of microwave plasma sources and, in particular, to a modular microwave plasma source that includes solid state electronics and an applicator for coupling the microwave radiation to a gas to form a plasma.
2) Description of Related Art
Plasma processing is used extensively in the manufacture of many different technologies, such as those in the semiconductor industry, display technologies, microelectromechanical systems (MEMS), and the like. Currently, radio frequency (RF) generated plasmas are most often used. However, plasmas generated with a microwave source allow for denser plasmas and/or plasmas with a high concentration of excited neutral species. Unfortunately, plasmas generated with a microwave source also suffer their own drawbacks.
Typical microwave plasma systems use a singular, large source of microwave radiation (typically a magnetron) and a transmission path for guiding the microwave radiation from the magnetron to the processing chamber. For typical high power applications in the semiconductor industry, the transmission path is a microwave waveguide. Waveguides are used because outside of a waveguide designed to carry the specific frequency of the microwave source, the microwave power attenuates rapidly with distance. Additional components, such as tuners, couplers, mode transformers, and the like are also required to transmit the microwave radiation to the processing chamber. These components limit the construction to large systems (i.e., at least as large as the sum of the waveguide and associated components), and severely limit the design. As such the geometry of the plasma that may be produced is constrained since the geometry of the plasma resembles the shape of the waveguides. Accordingly, it is difficult to match the geometry of the plasma to the geometry of the substrate that is being processed. In particular, it is difficult to create a microwave plasma where the plasma is generated over the entire surface of the wafer of larger substrates (e.g., 300 mm or greater wafers). Some microwave generated plasmas may use a slot line antenna to allow the microwave energy to be spread over an extended surface. However, such systems are complicated, require specific geometry, and are limited in the power density that can be coupled to the plasma.
Furthermore, microwave sources typically generate plasmas that are not highly uniform and/or are not able to have a spatially tunable density. As the substrates that are being processed continue to increase in size, it becomes increasingly difficult to account for edge effects. Additionally, the inability to tune the plasma limits the ability to modify processing recipes to account for incoming substrate nonuniformity and adjust the plasma density for processing systems in which a nonuniformity is required to compensate for the design of the processing system (e.g., to accommodate the nonuniform radial velocity of the rotating wafers in some processing chambers).